Every country regulates immigration in its own imperfect way. Some countries have populations that are 80 percent foreign-born but offer no pathway to permanency. Other countries put up huge barriers to citizenship except for people whose parents were born there.

President Trump has called for a shift from what currently makes the American immigration system distinct: its focus on family ties, a framework that accounts for two-thirds of all residency visas, more than any other country. Instead, he and many Republicans would like most visas to be distributed based on employability, with a preference for those who are highly skilled, like doctors, engineers or entrepreneurs.

“In many ways the U.S. immigration system is a relic of the past,” said Justin Gest, a professor at George Mason University who studies comparative immigration policy, referring to how public opinion has changed since 1965, when the family-based system was established. “It is far more generous than I think the spirit of the United States is today.”

The accompanying chart displays selected countries and the circumstances under which each one welcomes foreigners. It’s based on data from 2011, the latest year available for certain countries like China, and shows temporary migrants (like students and guest workers) and permanent migrants, broken down by the basis for their visa: family ties, employment, humanitarian purposes (as with refugees) or under a free-movement policy (as with the European Union).

Note that the data did not capture undocumented immigrants. Although the United States has good estimates on its undocumented population, data from other countries are spotty and harder to come by.

Simply put, the purpose of an immigration policy is to decide what types of people to allow inside the border. What would it look like if the United States adopted rules more like those of Canada, Japan or Qatar? Compare the policies below.

The Mix if We Looked More Like Canada

How many people?

Immigrants in 2011 as a percentage of the population

For what reason?

Types of immigrants as a share of all immigrants that year

In 2011, Canada and Australia relied heavily on immigrants who were admitted based on employability, many of whom were allowed to stay permanently. Both countries used a merit-based point system to determine who qualified, assigning a number of points to criteria such as education, language skills and employment history.

Mr. Trump has said that he would like to emulate the Canadian and Australian systems. But Mr. Gest pointed to a blind spot the size of Ohio — the seventh-most populous state — that could be obscuring how similar the systems already are: undocumented immigrants, who are highly represented in the United States in many low-skill industries like farming and construction.

“If you think of the undocumented as 11 to 12 million temporary low-skilled laborers, then you have a system that looks a little bit more like Canada” in terms of temporary workers, he said. (In fact, Canada and Australia have a much greater proportion of temporary workers than the United States.)

But a merit-based system doesn’t necessarily result in economic payoff, because skills don’t always lead to a job. For example, Canada has struggled to keep its merit-based workers employed since 1967, when the policy was first established.

That’s because some of the very skills and credentials that ushered immigrants into the country were unrecognized once they arrived, so many ended up unemployed or underemployed.

Another reason President Trump might not want to rely too heavily on Canada or Australia as models: Both countries allow in far more immigrants as a percentage of their population. If the United States were to follow their lead, it would involve admitting millions more people.

Or More Like Europe

How many people?

Immigrants in 2011 as a percentage of the population

For what reason?

Types of immigrants as a share of all immigrants that year

Historically, most immigrants in Europe have been other Europeans. The European Union allows people to relocate between countries with a level of freedom that is unmatched elsewhere in the world, greatly widening employment pools.

Middle Eastern conflict has created an exception in recent years, spurring a big influx of asylum seekers from war-torn countries. But humanitarian migrants typically make up only a small proportion of Europe’s foreign-born population.

Mercosur, a trade bloc in South America, functions like the E.U., though it allows people to live outside their home countries for only two years at a time, after which they must apply for permission to stay permanently.

It might help to imagine that these partnerships are like Nafta — the policy between the United States, Mexico and Canada that lowers barriers for trade, which President Trump has threatened to eliminate — but instead of goods, the agreements apply to people.

In a system like that, Americans looking for work would be able to expand their searches into Canada and Mexico, but they would also compete against Canadian and Mexican candidates for jobs in the United States.

Or Like Japan and South Korea

How many people?

Immigrants in 2011 as a percentage of the population

For what reason?

Types of immigrants as a share of all immigrants that year

South Korea and Japan are so stringent with immigration that they make the United States look lenient. This is partly because of a desire to preserve their cultures, a goal echoed by some conservative groups in the United States.

For example, the Japanese government once offered thousands of dollars to immigrants of Japanese descent to leave the country. And very few people become South Korean citizens without family ties; doing so requires years of residence, an in-person language proficiency test and a written test on customs, history and culture.

On top of stoking racial tensions, these policies have created demographic problems for South Korea and Japan. Both countries’ populations are agingrapidly, social services are underfunded, and many industries face labor shortages.

Some unusual policies, such as Japan’s practice of granting citizenship based on a parent’s Japanese nationality instead of where babies are born, have created situations where three generations of a family may not be Japanese citizens despite having lived in the country all their lives.

Or Like the Gulf States

How many people?

Immigrants in 2011 as a percentage of the population

For what reason?

Types of immigrants as a share of all immigrants that year

The Gulf states allow a huge immigrant influx to meet the demand for cheap, low-skilled labor, but almost all of the immigrants are temporary, and they have few rights or protections.

In Qatar, for example, roughly 80 percent of the population is foreign-born. Without them, the skyscrapers of Doha or the 2022 World Cup, for which the government has promised to build more than half a dozen new stadiums, would not be possible. And the Qatari government has been accused of human rights abuses against those workers.

The only way that governments can sustain these heavy immigrant populations is by withholding the generous resources that are granted to ordinary citizens, such as free health care, free college tuition and marriage allowances.

Most Americans would not be comfortable with this approach, said Morris Levy, a political scientist at the University of Southern California who studies public opinion on immigration. “People dislike the idea of a permanent second-class citizen,” he said. “It goes back to a core set of values that people think of as really elemental to being American.”

The Future Is Probably Somewhere in the Middle

Based on the current debate, any solution that Congress agrees on will probably fall somewhere between international models. It could follow some trends that are occurring worldwide.

For example, in many countries, including Canada and Australia, there has been a shift away from exclusively merit-based systems to ones that also consider whether someone has a job offer — something currently done in the United States.

For purposes of immigration, the United States could narrow its definition of family, which is wider than that of any other country, to exclude siblings or adult children who are married.

Although current American policies around family-based migration are the most generous in the world, the results look much different in practice because of limits on the number of visas that can be granted in each category.

“There is a certain mindlessness to family immigration when you take into account eligibility and time,” said Demetrios G. Papademetriou, co-founder of the Migration Policy Institute, a research organization. “Someone qualifies, but it may take 20 years before a visa is open to them.”

“There is a major undisputed advantage to family immigration, chain migration; it’s become apparently a dirty word,” he said. “You have someone here who will show you the ropes, who will take you in that can set up employment for you. When it comes to immigrant integration, family is very important.”

You could envision a merit-based system that incorporates characteristics of our current system. It could grant points to people who have family members in the United States, or who come from countries that are not highly represented in the current population.

In that case, it might be desirable to pay attention to the weight each category is given and to adjust based on economic and social outcomes.

“That is how you keep a point selection system,” Mr. Papademetriou said. “Everything else is just blind faith or politics. Our system that exists today is just politics.”

While the sputtering negotiations are frustrating for many people, especially for those caught up in the system, academics agree that, in general, these decisions should not be rushed.

“Immigration is social engineering,” said Mr. Gest, the George Mason University professor. “You’re building the population of the future.”